The present applicant has already advanced various proposals on cycloolefin random copolymers formed from ethylene and specific cycloolefins, for example, in Japanese Patent L-O-P Publn. No. 168708/1985, and Japanese Patent Application Nos. 220550/1984, 236828/1984, 236829/1984 and 242336/1984. The cycloolefin copolymers thus proposed have excellent transparency and are also excellent in various characteristics such as heat resistance, thermal aging resistance, chemical resistance, solvent resistance, dielectric characteristics and mechanical characteristics. Further, these cycloolefin random copolymers are also excellent in adhesive properties to structures of various kinds of materials, though said random copolymers are considered as a kind of polyolefin Accordingly, these cycloolefin random copolymers have such characteristics basically suitable for use as the resins for forming substrates for information recording media or forming optical instruments such as optical fibers.
The cycloolefin random copolymers as mentioned above possess characteristics suitable basically for use as the resins for forming optical instrument parts. After thorough investigations, however, it was found that when the above-mentioned cycloolefin random copolymers are used for forming substrates for information recording media, for example, optical memory disc, CD disc and laser disc, the moldability attained at the time of molding these copolymers into a disc or the transferability of the recorded information from a master disc to a fresh disc is not always satisfactory. That is, in an information recording medium such as an optical memory disc, CD disc or laser disc, which is used exclusively for reproduction purposes, information is recorded therein by corresponding the existence or nonexistence of the pit formed on the disc substrate to a signal of "0" or "1". In order to prepare a substrate having a recorded information thereon, there is usually employed a molding method in which a resin is injection molded into a substrate using a master disc. If the resin used in the process mentioned above is low in flowability, no satisfactory transfer of the pit from the master disc to a fresh disc is attained sometimes and thereby causing an error in reading of the disc obtained, because the pit usually has such a very small diameter as of not more than 1 .mu.m, and said resin is found to be poor in moldability. On the other hand, the transferability of the pit is improved if a resin having a high flowability is used, but the resulting disc substrate is deteriorated sometimes in mechanical characteristics.
Under such circumstances, as mentioned above, the present inventors found that resin compositions which are high in moldability and also excellent in transferability of the pit are obtained by using a blend of at least two kinds of cycloolefin random copolymers in such a manner that the specific requirements defined in the present invention are satisfied, and eventually have accomplished the invention.